The present invention relates generally to the desulfurization of fuel gases by the removal of sulfur species from a hot fuel gas stream produced by the gasification of a carbonaceous fuel. More particularly, the present invention relates to the removal of sulfur species from such hot fuel gas by using a fluidized bed of particulate sorbent wherein sulfur-laden sorbent in the fluidized bed is continuously removed from the fluidized bed, regenerated in a riser tube with an oxygen-containing gas and returned to the fluidized bed.
The gasification of carbonaceous fuels, especially coal, in an oxygen deficient or reducing atmosphere is frequently utilized to produce hot, fuel-rich fuel gases which provide a combustible driving fluid for various types of prime movers and as a combustible fuel useful in other heat utilizing applications.
A significant problem attendant with the use of fuel gas produced in the gasifiers is due to the presence of sulfur species, primarily hydrogen sulfide, carbonyl sulfide, and carbon disulfide, in the fuel gas which are environmental pollutants and cause deleterious build-ups in equipment and contaminate processes capable of utilizing the fuel gas. The removal of sufficient sulfur species from the fuel gas to provide the latter with acceptable sulfur levels has been successfully accomplished by utilizing various sulfur sorbents such as calcium compounds in the gasifier and/or particulate sorbent-containing beds contactable by the fuel gas discharged from the gasifier.
The desulfurization of hot fuel-rich or oxygen-deficient fuel gases derived from the gasification of sulfur-bearing fuels by utilizing particulate sorbent-containing beds has been found to be particularly desirable because of the high sorbing efficiency of the sorbent and the fact that many of the presently known sorbents useful as bed material can be readily regenerated. Solid sorbents in particulate form found to be satisfactory as sulfur sorbents in fixed-, moving-, and fluidized-bed contactors or absorbers for removing sulfur species and compounds from hot fuel gas include iron oxide, zinc ferrite, zinc titanate, zinc oxide, and in combinations thereof. These sorbents may also be satisfactorily supported on bases such as alumina or zeolites.
As previously practiced, the regeneration of sulfur-bearing particulate sorbents was achieved by taking the contactor containing the bed of sorbent off line or by removing the sorbent from the contactor to a separate regeneration vessel. The regenerating sorbent in the off line contactor or in the separate regeneration vessel is achieved by passing a hot oxygen-containing regeneration gas through the hot sorbent for effecting an exothermic reaction between the sulfur compounds absorbed or captured by the sorbent and the oxygen in the gas to form sulfur oxides, primarily sulfur dioxide and sulfur trioxide, which are entrained in the regeneration gas. After regeneration the contactor is put back on line or the regenerated sorbent is returned from the separate vessel to the contactor for subsequent capture of sulfur species from the hot fuel gas. The sulfur oxide laden gas resulting from regeneration of the sorbent is readily treated for producing elemental sulfur or disposable, environmentally stable sulfur compounds.